The Spanish shepherd boy Santiago (actually he's in his late teens) has a dream of treasure near the Pyramids. Should he believe his dream? He meets a man who gives him the advice that when you want something, all the universe conspires in helping you to achieve it. Strangely similar to a quote from Ralph Waldo Emerson. Now I read somewhere that Emerson deserved to be shot for his quote about mousetraps, and this advice didn't seem very helpful either. Santiago sells his flock and starts a journey to Egypt, but soon all his money is stolen - hardly things conspiring in his favour. He has to try to earn enough to restart a flock.
But does Santiago ever find his treasure by the Pyramids? You'll need to read the book to find out. The point the book does make is that if you really want to do something but don't, then you'll live to regret it - much more than if you go ahead but run into problems. A lesson you can learn from other books perhaps, but Coelho's enchanting fable is still well worth reading.